This application relates to an improved collapsible mold core which permits the manufacture of straight-walled buckets, for example, in which the bucket lip has an inwardly-projecting rim that would seriously interfere with the removal of the bucket from a noncollapsible core. The collapsible mold core may also be used for the manufacture of any other desired molded device, particularly those having inwardly projecting members so that a collapsible core is required.
In U.S. Pat. No. 4,286,766 a collapsible mold core is disclosed having an inner core member of the shape of a conical section, surrounded by eight sliding members which fit around the conical core and slide in longitudinal manner along the core between the collapsed and molding positions to first permit the molding of a bucket and then to permit its removal as the core moves between its respective two positions.
In the mold core of the above-cited patent, the eight outer core elements comprise four larger outer core elements and four smaller outer core elements arranged in alternating sequence about the conical inner core. The smaller of the outer core elements are generally triangular in cross section, with their two inwardly-facing angles defining delicate feather edges, because the inner core-facing surfaces of these smaller outer core members are concave in shape, so that their angular edges define a very small angle. Such parts are difficult to manufacture with good accuracy because of the difficulty of machining the concave surfaces, and also they are subject to wear and breakage because of the inherent fragility of the feather edges.
In accordance with this invention an improved collapsible mold core is provided having an inner core member and a plurality of outer core members which slide longitudinally along the inner core member. However, in accordance with this invention, the outer core member parts are easier to fabricate, having fewer curved surfaces, and also are sturdier since they do not require the feather edge of the previous design. Likewise, by this invention, only six outer core elements are required rather than the eight outer core elements of the prior art, resulting in a significant reduction in the cost and complexity of the collapsible core.
Furthermore, in accordance with this invention, means are provided for forming a seal groove about the bucket lip with apparatus that permits the easy and automatic removal of the freshly molded bucket from the seal groove-forming fixture. In the past this has proven to be a difficulty in that the newly molded seal groove can be tightly retained in its fixture, and the bucket could not be easily removed by pneumatic means, which is desirable. A freshly molded, large bucket is still rather soft, and mechanical punch out members can warp and even punch through the bucket during the removal process, since the plastic of the bucket is not completely hardened.
The mold core of this invention also may have water cooling means in the inner core member and all of the outer core members, permitting faster operation.